How can i plot multiple objects in same 3D space i.e. plot3 ?

I need to visualize multiple objects i.e. 2D circle and 2D ellipse in same 3d space (plot3)..

i have shared codes of both cirle and ellipse .. please guide me.

%CODE FOR 2D CIRCLE IN 3D SPACE

center = [0.5 0 0.4]; %[x y z]
radius = 0.1;

dt = 0.25;
t = (0:dt:10)';
theta = t*(2*pi/t(end))-(pi/2);
points = center + radius*[0*ones(size(theta)) cos(theta) sin(theta)];

hold on;
plot3(points(:,1),points(:,2),points(:,3),'-*w', 'LineWidth', 0.002);
xlabel('x');
ylabel('y');
zlabel('z');
axis auto;
view([60,10]);
grid('minor');

%CODE FOR 2D ELLIPSE IN 3D SPACE

gtobj=ellipticalFit.groundtruth([], [0,0],[0.075,0.15]/2,90); %Define the ellipe in 2D
xy=gtobj.sample(0:20:360); %Define waypoint coordinates
axis auto; 
view([-41,-33])
hEllipse=plot(gtobj,{'Color','g'});  %Make plot in xy plane first
hold on
hWayPts=scatter(xy{:},'filled','k','SizeData',50);
hold off
xlabel 'X', ylabel 'Y', zlabel 'Z'
T=makehgtform('translate',[0.4,0,0.4],'yrotate',pi/2); %rototranslate the plot out of xy plane
set([hEllipse,hWayPts],'Parent',hgtransform('Matrix',T))

[Matt J]

Note that ellipticalFit() can be a helpful tool for plotting ellipses, but as I told you in an earlier thread you have to download it!

https://www.mathworks.com/matlabcentral/fileexchange/32108-fitting-a-conic-to-a-given-set-of-points-using-levenberg-marquardt-method

Answer 1

[DGM]

Something like this?

center = [0.5 0 0.4]; %[x y z]
radius = 0.1;
dt = 0.25;
t = (0:dt:10)';
theta = t*(2*pi/t(end))-(pi/2);
points = center + radius*[0*ones(size(theta)) cos(theta) sin(theta)];
hold on;
plot3(points(:,1),points(:,2),points(:,3),'-*r', 'LineWidth', 0.002);

% what is this?  
% gtobj=ellipticalFit.groundtruth([], [0,0],[0.075,0.15]/2,90); 
% since i can't plot something i don't have, i'll just plot another circle
center = [0.5 0 0.4]; %[x y z]
radius = 0.08;
dt = 0.25;
t = (0:dt:10)';
theta = t*(2*pi/t(end))-(pi/2);
points = center + radius*[cos(theta) 0*ones(size(theta)) sin(theta)];
plot3(points(:,1),points(:,2),points(:,3),'-*b', 'LineWidth', 0.002);

% wait until the plots are done to add the labels and stuff
xlabel('x');
ylabel('y');
zlabel('z');
axis equal
view([60,10]);
grid('minor');

I have no idea what ellipticalFit.groundtruth is, I can't demonstrate it.

Answer 2

[Matt J]

Using hold on and hold off, you can add anything you want to a pre-existing 3D axis, even the results of a 2D plotting command. The result of a 2D plotting command will be placed in the xy-plane. (Note that some plotting commands like line() or surface() will add to an existing axis without the need to issue hold.)

Once you have added a 2D plot to a 3D axis, you can re-orient it arbitrarily in 3D space using hgtransform. So for example, your 3D circle could also have been generated using the 2D plot() command as follows:

center = [0.5 0 0.4]; %[x y z]
radius = 0.1;
dt = 0.25;
t = (0:dt:10)';
theta = t*(2*pi/t(end))-(pi/2);


xlabel('x');
ylabel('y');
zlabel('z');
axis auto;
view([60,10]);
grid('minor');


hold on 
T=makehgtform('translate',center,'yrotate',pi/2);
plot(radius*cos(theta),radius*sin(theta),'-*r',  'Parent', hgtransform('Matrix',T))
hold off

I should caution you that hgtransform has shown some quirky behavior in R2020b as discussed in this thread,

https://www.mathworks.com/matlabcentral/answers/769387-understanding-implicit-surface-plot-behavior?s_tid=srchtitle

Basically though, as long as you do not modify the axes limits after the hgtransform is created, you should be fine.

[Matt J]

For an ellipse, it's the same kind of thing,

hold on 
axis vis3d;
T=makehgtform('translate',center,'yrotate',pi/2);
plot(2*radius*cos(theta),radius*sin(theta),'-*r',  'Parent', hgtransform('Matrix',T))
hold off